1. Field of the Invention
The present invention relates to an improvement of an in-vehicle engine control apparatus for injecting a fuel for a plurality of times in one combustion cycle of an internal combustion engine, and more particularly, to an in-vehicle engine control apparatus for suppressing a temperature increase in a fuel injection control unit resulting from the plurality of injections.
2. Description of the Related Art
In a fuel injection multi-cylinder engine, exhaust gas purification and an increase in fuel efficiency that are suited to a load state are carried out by, for example, a batch injection method of carrying out the fuel injection once in one combustion cycle of each cylinder, a split injection method of carrying out a plurality of split injections to inject the same amount of fuel in total, and an intermittent split injection method of alternately repeating the batch injection and the split injection.
Note that, the split injection includes various forms ranging from a two-split injection, which includes an early-stage fuel injection in the intake stroke and a late-stage fuel injection in the compression stroke, up to the maximum five-split injection, which includes a pilot injection in the compression stroke, a pre injection, a main injection, and an after injection in the power stroke, and a post injection in the exhaust stroke.
For example, according to FIG. 3, FIG. 4, and FIG. 8 of Japanese Patent Application Laid-open No. 2005-337038, which is titled “Fuel injection control apparatus”, the following configuration is disclosed. Specifically, among a plurality of charge FETs 35 (boost switching devices according to the present invention) for generating boosted high voltages, four separation FETs 36 (quick power supply switching devices according to the present invention) for applying the boosted high voltages to a plurality of injectors 20, and constant current FETs 37 (power supply switching devices according to the present invention) for supplying power from a battery power supply to the injectors 20, a thermistor 41 for detecting an ambient temperature Ta of those FETs 35 to 37 is provided. Further, a temperature difference between the ambient temperature Ta in a case of an operation under the severest condition and a junction temperature Tj of each of the FETs 35 to 37 is calculated and stored in advance, a maximum junction temperature Tjmax is calculated by adding each of the temperature differences to the actual ambient temperature Ta, and when the maximum junction temperature Tjmax is more than a predetermined temperature (such as 150° C.) for determining an overheat state, the number of split stages (up to five stages) of the split injections is decreased. In this manner, an increase in temperature is suppressed.
Moreover, according to FIG. 10A and FIG. 10B and descriptions of paragraphs [0055] and [0056], such a description is made that the thermistor 41 is preferably provided so as to be in close contact with a heatsink of the MOSFETs that are components subject to the measurement to measure the ambient temperature Ta at the closest location, and calculation errors in the junction temperatures are consequently reduced.
The fuel injection control apparatus disclosed in Japanese Patent Application Laid-open No. 2005-337038 is configured such that injection thermistor 41 for detecting the closest ambient temperature Ta of the FETs, which are the switching devices subject to the temperature monitoring, is provided, and the number of injection stages are limited so that the junction temperatures of the switching devices calculated and estimated therefrom are equal to or less than the predetermined temperature.
However, while the fuel injection control apparatus is generally installed in an engine room and it is necessary to assume that the temperature in the engine room increases up to 120° C., in order to maintain the junction temperature of the semiconductor devices to be equal to or less than 175° C., the temperature of the heat sink unit representing the internal temperature of the semiconductor devices needs to be managed to be equal to or less than 150° C.
Thus, an increase in the internal temperature permitted for the switching devices in the fuel injection control apparatus is equal to or less than 20° C. to 30° C., and even when the closest temperature of the switching devices is detected, a distribution between the environmental temperature and the temperature increase caused by the self-heat generation, which form the closest temperature, is not detected, and hence there is a problem in that the temperature increase amount of the switching devices cannot be accurately managed, and even when the actual temperature increase is smaller, only control having a margin, which is based on the maximum temperature increase value acquired by assuming the worst state, can be carried out.